Nitrogen and sulfur co-doped vanadium carbide MXene for highly reversible lithium-ion storage.

As an emerging group of two-dimensional (2D) layered material, MXenes have received significant attention in the direction of energy storage. However, the restacking of MXene flakes severely hinders the ion transport within electrodes, which limits their application for lithium-ion batteries (LIBs). To address this issue, herein, we rationally designed and optimized the structure of N, S co-doped V2CTx MXene, which exhibits excellent electrochemical performance with a high reversible capacity of 590 mAh g-1 after 100 cycles at 0.1 A g-1 when used as anode of LIBs. Even at a high current density of 2 A g-1, a reversible capacity of 298 mAh g-1 is obtained after 300 cycles, which outperforms most of the V2CTx-based anode materials reported so far. The lithium-ion storage mechanism of N, S co-doped V2CTx MXene was studied by a series of characterizations. The results show that the significant improvement of electrochemical performance should be attributed to the facilitated charge transfer after N and S co-doping in V2CTx MXene, which can effectively improve the ion transfer kinetics during the lithiation-delithiation process. Furthermore, the expanded interlayer spacing of N, S co-doped V2CTx provides more active sites for the adsorption of lithium ions, promoting the insertion capacity of lithium ions. This work indicates that the N, S co-doped 2D V2CTx MXene should be a promising anode material for high-performance LIBs.